ipc: fix wrong comments

This patch fixes the wrong / obsolete comments in the ipc code.  Also adds
a missing lock around ipc_get_maxid() in shm_get_stat().

Signed-off-by: Nadia Derbey <Nadia.Derbey@bull.net>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 50 insertions, 28 deletions

diff --git a/ipc/util.c b/ipc/util.c
index 49e75efe305b..fd29246dc3c8 100644
--- a/ipc/util.c
+++ b/ipc/util.c
@@ -194,7 +194,7 @@ void __init ipc_init_proc_interface(const char *path, const char *header,
  *      Requires ipc_ids.mutex locked.
  *      Returns the LOCKED pointer to the ipc structure if found or NULL
  *      if not.
- *      If key is found ipc contains its ipc structure
+ *      If key is found ipc points to the owning ipc structure
  */
  
 static struct kern_ipc_perm *ipc_findkey(struct ipc_ids *ids, key_t key)
@@ -258,10 +258,10 @@ int ipc_get_maxid(struct ipc_ids *ids)
  *      @new: new IPC permission set
  *      @size: limit for the number of used ids
  *
- *      Add an entry 'new' to the IPC idr. The permissions object is
+ *      Add an entry 'new' to the IPC ids idr. The permissions object is
  *      initialised and the first free entry is set up and the id assigned
- *      is returned. The list is returned in a locked state on success.
- *      On failure the list is not locked and -1 is returned.
+ *      is returned. The 'new' entry is returned in a locked state on success.
+ *      On failure the entry is not locked and -1 is returned.
  *
  *      Called with ipc_ids.mutex held.
  */
@@ -270,10 +270,6 @@ int ipc_addid(struct ipc_ids* ids, struct kern_ipc_perm* new, int size)
 {
         int id, err;
 
-        /*
-         * rcu_dereference()() is not needed here since
-         * ipc_ids.mutex is held
-         */
         if (size > IPCMNI)
                 size = IPCMNI;
 
@@ -303,12 +299,12 @@ int ipc_addid(struct ipc_ids* ids, struct kern_ipc_perm* new, int size)
 /**
  *      ipcget_new      -       create a new ipc object
  *      @ns: namespace
- *      @ids: identifer set
+ *      @ids: IPC identifer set
  *      @ops: the actual creation routine to call
  *      @params: its parameters
  *
- *      This routine is called sys_msgget, sys_semget() and sys_shmget() when
- *      the key is IPC_PRIVATE
+ *      This routine is called by sys_msgget, sys_semget() and sys_shmget()
+ *      when the key is IPC_PRIVATE.
  */
 int ipcget_new(struct ipc_namespace *ns, struct ipc_ids *ids,
                 struct ipc_ops *ops, struct ipc_params *params)
@@ -330,9 +326,16 @@ int ipcget_new(struct ipc_namespace *ns, struct ipc_ids *ids,
 /**
  *      ipc_check_perms -       check security and permissions for an IPC
  *      @ipcp: ipc permission set
- *      @ids: identifer set
  *      @ops: the actual security routine to call
  *      @params: its parameters
+ *
+ *      This routine is called by sys_msgget(), sys_semget() and sys_shmget()
+ *      when the key is not IPC_PRIVATE and that key already exists in the
+ *      ids IDR.
+ *
+ *      On success, the IPC id is returned.
+ *
+ *      It is called with ipc_ids.mutex and ipcp->lock held.
  */
 static int ipc_check_perms(struct kern_ipc_perm *ipcp, struct ipc_ops *ops,
                         struct ipc_params *params)
@@ -353,12 +356,16 @@ static int ipc_check_perms(struct kern_ipc_perm *ipcp, struct ipc_ops *ops,
 /**
  *      ipcget_public   -       get an ipc object or create a new one
  *      @ns: namespace
- *      @ids: identifer set
+ *      @ids: IPC identifer set
  *      @ops: the actual creation routine to call
  *      @params: its parameters
  *
- *      This routine is called sys_msgget, sys_semget() and sys_shmget() when
- *      the key is not IPC_PRIVATE
+ *      This routine is called by sys_msgget, sys_semget() and sys_shmget()
+ *      when the key is not IPC_PRIVATE.
+ *      It adds a new entry if the key is not found and does some permission
+ *      / security checkings if the key is found.
+ *
+ *      On success, the ipc id is returned.
  */
 int ipcget_public(struct ipc_namespace *ns, struct ipc_ids *ids,
                 struct ipc_ops *ops, struct ipc_params *params)
@@ -389,6 +396,10 @@ int ipcget_public(struct ipc_namespace *ns, struct ipc_ids *ids,
                         if (ops->more_checks)
                                 err = ops->more_checks(ipcp, params);
                         if (!err)
+                                /*
+                                 * ipc_check_perms returns the IPC id on
+                                 * success
+                                 */
                                 err = ipc_check_perms(ipcp, ops, params);
                 }
                 ipc_unlock(ipcp);
@@ -401,12 +412,9 @@ int ipcget_public(struct ipc_namespace *ns, struct ipc_ids *ids,
 
 /**
  *      ipc_rmid        -       remove an IPC identifier
- *      @ids: identifier set
- *      @id: ipc perm structure containing the identifier to remove
+ *      @ids: IPC identifier set
+ *      @ipcp: ipc perm structure containing the identifier to remove
  *
- *      The identifier must be valid, and in use. The kernel will panic if
- *      fed an invalid identifier. The entry is removed and internal
- *      variables recomputed.
  *      ipc_ids.mutex and the spinlock for this ID are held before this
  *      function is called, and remain locked on the exit.
  */
@@ -558,10 +566,12 @@ static void ipc_do_vfree(struct work_struct *work)
  */
 static void ipc_schedule_free(struct rcu_head *head)
 {
-        struct ipc_rcu_grace *grace =
-                container_of(head, struct ipc_rcu_grace, rcu);
-        struct ipc_rcu_sched *sched =
-                        container_of(&(grace->data[0]), struct ipc_rcu_sched, data[0]);
+        struct ipc_rcu_grace *grace;
+        struct ipc_rcu_sched *sched;
+
+        grace = container_of(head, struct ipc_rcu_grace, rcu);
+        sched = container_of(&(grace->data[0]), struct ipc_rcu_sched,
+                                data[0]);
 
         INIT_WORK(&sched->work, ipc_do_vfree);
         schedule_work(&sched->work);
@@ -650,7 +660,7 @@ void kernel_to_ipc64_perm (struct kern_ipc_perm *in, struct ipc64_perm *out)
 }
 
 /**
- *      ipc64_perm_to_ipc_perm  -       convert old ipc permissions to new
+ *      ipc64_perm_to_ipc_perm  -       convert new ipc permissions to old
  *      @in: new style IPC permissions
  *      @out: old style IPC permissions
  *
@@ -669,6 +679,18 @@ void ipc64_perm_to_ipc_perm (struct ipc64_perm *in, struct ipc_perm *out)
         out->seq        = in->seq;
 }
 
+/**
+ * ipc_lock - Lock an ipc structure
+ * @ids: IPC identifier set
+ * @id: ipc id to look for
+ *
+ * Look for an id in the ipc ids idr and lock the associated ipc object.
+ *
+ * ipc_ids.mutex is not necessarily held before this function is called,
+ * that's why we enter a RCU read section.
+ * The ipc object is locked on exit.
+ */
+
 struct kern_ipc_perm *ipc_lock(struct ipc_ids *ids, int id)
 {
         struct kern_ipc_perm *out;
@@ -771,8 +793,8 @@ static void *sysvipc_proc_next(struct seq_file *s, void *it, loff_t *pos)
 }
 
 /*
- * File positions: pos 0 -> header, pos n -> ipc id + 1.
- * SeqFile iterator: iterator value locked shp or SEQ_TOKEN_START.
+ * File positions: pos 0 -> header, pos n -> ipc id = n - 1.
+ * SeqFile iterator: iterator value locked ipc pointer or SEQ_TOKEN_START.
  */
 static void *sysvipc_proc_start(struct seq_file *s, loff_t *pos)
 {
@@ -807,7 +829,7 @@ static void sysvipc_proc_stop(struct seq_file *s, void *it)
         struct ipc_proc_iface *iface = iter->iface;
         struct ipc_ids *ids;
 
-        /* If we had a locked segment, release it */
+        /* If we had a locked structure, release it */
         if (ipc && ipc != SEQ_START_TOKEN)
                 ipc_unlock(ipc);